Alzheimer's disease (AD) is an age-related brain disorder that develops over many years. Its symptoms typically first appear after age 60. The course of AD varies from person to person, but in most people, the first symptom is memory loss. Memory decline becomes more serious as the diseas progresses, and people often begin having problems with other cognitive functions, such as decision making (including financial) and language skills. People with Alzheimer's may also experience behavior and personality changes. Eventually, the loss of mental function becomes so severe that it impairs daily living and the ability to recognize family and friends. These losses are related to the breakdown of the connections between different classes of neurons (nerve cells) in the brain and the associated death of many of these cells.

Although AD was first described by Dr. Alois Alzheimer more than 100 years ago, scientific study of the disease began in earnest only in the early 1970s.